The present invention relates to a magneto-optical recording medium, and more specifically to a magneto-optical recording medium suitable in use for magnetic field modulation recording.
The recording technique by use of the magneto-optical recording medium may be roughly classified into light modulation recording technique and magnetic field modulation recording technique. The magnetic field modulation recording is easy to overwrite data in the recording medium, and suitable for mark edge recording. In the magnetic field modulation recording, however, since a magnetic head is required, it is necessary to reduce the inductance of the head and further to switch a large current so that the magnetic field may be switched at high speed. In addition, the intensity of the magnetic field applied to the recording layer of the recording medium must be increased as much as possible, by arranging the magnetic head as close as possible to the recording layer thereof. For this purpose, it is practically effective to use a flying magnetic head, as disclosed in Japanese Published, Unexamined (Kokai) Patent Application No. 63-217548.
In any cases, however, it is preferable to reduce the intensity of the magnetic field required to be applied to the recording layer of the recording medium, that is, to record data in the magneto-optical recording medium in accordance with the magnetic field modulation recording in a low magnetic field. Therefore, various countermeasures have been so far proposed as follows: a fourth element, such as, Nd, is added to the recording medium to improve the characteristics thereof in a low magnetic field, as disclosed by DIGEST of 11 th Annual Conference on Magnetics in Japan, page 268; magnetic layers of different compositions are exchange-coupled to decrease a stray magnetic field and thereby to improve the response speed to an external magnetic field, as disclosed in Japanese Published, Unexamined (Kokai) Patent Application No. 62-128040; a perpendicular magnetization film, i.e., a film having an easy perpendicular axis of magnetization and an in-plane magnetization film, i.e., a film having an easy in-plane axis of magnetization, are laminated to concentrate the magnetic flux effectively to the perpendicular magnetization film and thereby to reduce the intensity of the modulated magnetic field, as disclosed in Japanese Published, Unexamined (Kokai) Patent Application No. 61-188758; or a TbFeCo layer is deposited with a GdFeCo layer, which is lower in perpendicular magnetization anisotropy than TbFeCo or DyFeCo, in order to limit the stability of micro domains and thereby to improve the magnetic field sensitivity, as disclosed in Japanese Published, Unexamined (Kokai) Patent Application No. 1-281239.
In the conventional recording techniques so far proposed, however, it has been difficult to reduce the intensity of the modulated magnetic field down to below .+-.100 Oe, and further there exists a problem in that the reproduced signal characteristics are deteriorated when the fourth element is added to the recording medium or when the in-plane magnetization layer is laminated onto the recording medium. To overcome these problems, therefore, prior to this application, the same inventors have already found that it is possible to reduce the intensity of the modulated magnetic field by virtue of such a method of manufacturing a magneto-optical recording medium as to form a recording layer on a leveled underlayer, and this manufacturing method has been already filed as an application for patent. In addition, the same inventors have found that the same effect as above may be obtained by virtue of such a method of manufacturing a magneto-optical recording medium as to add a leveling process during the formation of the recording layer, and this manufacturing method has also been filed as an application for patent. In practice, however, it has been found that a satisfactory effect cannot be still obtained by only the process of leveling the underlayer. These applications of the inventors are Japanese Published, Unexamined (Kokai) Patent Application No. 5-266520, published Oct. 15, 1993; Japanese Published, Unexamined (Kokai) Patent Application No. 4-209205, published Oct. 29, 1993; and Japanese Published, Unexamined (Kokai) Patent Application No. 6-60450, published Mar. 4, 1994, which applications are incorporated herein by reference herein.
Accordingly, an object of this invention is to provide a magneto-optical recording medium employed for the magnetic field modulation recording, by which sufficient recording effect may be realized in spite of a lower intensity of the modulated magnetic field than is conventional, and the method of manufacturing the same recording medium.